Problem: 7 rubber stamps cost $6.93. Which equation would help determine the cost of 15 rubber stamps?
Solution: There are several equations that could help determine the cost, each with a slightly different approach. We can write the fact that 7 rubber stamps cost $6.93 as a proportion: $\dfrac{7}{\$6.93}$ Let $x$ represent the unknown cost of 15 rubber stamps. Since 15 rubber stamps cost $x$ , we have the following proportion: $\dfrac{15}{x}$ The cost changes along with the number of rubber stamps purchased, and so the two proportions are equivalent. $\dfrac{7}{\$6.93} = \dfrac{15}{x}$